1. Field of the Invention
The present invention relates to a flexible shaft coupling. The invention particularly relates to a flexible shaft coupling including two coupling flanges for connecting additional coupling members thereto and a stack of springelastic membranes mounted at an axial distance from the two coupling flanges and connected to the flanges by means of tightening bolts which are mounted alternatingly on a circle on one or the other of the coupling flanges. The stack of membranes is mounted on tightening sleeves and is held together by means of the tightening bolts. Spacer washers are arranged next to the stack of membranes.
2. Description of the Related Art
Flexible shaft couplings of the above-described type have the purpose to directly transmit rotary motion with the application of torque while compensating any misalignments of the shafts during operation. The compensation of shaft misalignments is effected by connecting the stack of membranes as a flexible element alternatingly or cardanically to the two flanges. As a result, the entire flange unit can be displaced axially as well as angularly. Thus, when two couplings are used, a parallel displacement can also be compensated because the couplings are capable of being deflected axially as well as radially. However, such a flexible shaft coupling only operates properly if the rotary motion is transmitted with as little play and imbalance as possible. This means that the manufacture of such a shaft coupling is extremely complicated and expensive when exact connections between the stack of membranes and the coupling flanges is to be ensured.
A flexible shaft coupling of the above-described type is known, for example, from U.S. Pat. No. 4,073,161. In this shaft coupling, a connection with as little play as possible is to be achieved by means of an interference fit obtained by means of tightening bolts, cylindrical tightening sleeves, flange-like, integrally connected spacer washers and additional spacer washers. The stack of membranes is mounted on the sleeve with high accuracy of fit and is held together between the spacer washers by means of tightening bolts. To obtain a connection completely without play, such an interference fit must be manufactured very exactly, i.e., the bores in the coupling flanges and in the membranes and the spacing between bores and the pitch circle diameter must be manufactured within very narrow tolerances. Since tolerances cannot be avoided during manufacturing, frequently bracing occurs during the assembly of such a coupling. Because of these tolerances resulting from production, it can also not be excluded that under torque application some of the bolt shafts and the bore walls are subjected to higher loads. As a result, in some of the bolt connections within the coupling system, impermissibly high stresses occur in the bores and shear forces occur, since the rotary motion and the load are not uniformly distributed over all the bolt connections. This may lead to a misalignment of the surrounding coupling flanges and to imbalances and wear.
Another shaft coupling of the above-described type is known from German Auslegeschrift 26 45 600. In this shaft coupling, a preassembled pack is formed by a stack of membranes together with a centering ring connected to tightening bolts. The centering ring has a finely finished circumferential surface which, together with a correspondingly finely finished circumferential surface of a flange, forms a cylindrical press or interference fit. This preassembled stack or unit is fastened alternatingly to one of the two flanges by means of tightening bolts, with the possible intermediate arrangement of guide sleeves. In this shaft coupling, the stack of membranes is held in a centered position by means of the centering ring, however, no measures are provided for compensating the play between the tightening bolts and the stack of membranes which play is due to manufacturing tolerances. When impact-like loads occur, the bolts may be displaced due to the play which leads to an additional imbalance.
In order to avoid the danger of misalignments and play and the resulting imbalances, it has been attempted to provide a shaft coupling which is completely free of play. In a shaft coupling known from European application 0,184,051, the play due to manufacturing tolerances is to be eliminated by means of a conical bolt shaft with a correspondingly conical expansion sleeve.
However, the above coupling has the disadvantage that stresses are introduced into the components through the bores during expansion, particularly into the stack of membranes. In addition, the cone of the bolt shaft and the conical bore in the expansion sleeve must be manufactured very precisely in order to obtain a uniform expansion because otherwise non-uniform tensions in the bores would occur over the thickness of the stack of membranes. These tensions would disadvantageously affect the operation of the coupling.
It is, therefore, the primary object of the present invention to provide a flexible shaft coupling of the abovedescribed type which is as much as possible completely free of play and imbalance. Simultaneously, the forces resulting from the torque to be transmitted are uniformly distributed over all bolt connections in order to obtain a greater power density, i.e., a higher transmittable torque with the same or smaller dimensions.